1. Field of the Invention
The present invention relates in general to air bag modules for vehicle safety. In particular, the present invention relates to an improved attachment arrangement for securing a decorative cover to the air bag housing and surrounding dashboard.
2. Description of the Related Art
Air bag passive restraint systems have gained increasing popularity in recent years. Such systems typically include one or more modules mounted within the passenger compartment of a vehicle. These modules include a gas generator, an inflatable cushion to receive the gas in the event of a collision, and a cover to prevent damage to the cushion prior to use.
It has become common to provide the cover as a decorative member which forms a part of the dashboard, steering wheel, seat, door, roof, etc. of the vehicle. Such covers include a frangible section, typically having reduced strength tear lines, to permit a section of the cover to move and allow the inflating bag to expand past the cover. The frangible section must of course be sufficiently strong to resist accidental opening prior to a collision. The strength of the frangible section therefore requires that relatively large forces be placed on the cover by the inflating bag before the frangible section releases. This creates a danger that the force will cause the entire cover to be torn from the dashboard, possibly striking the passenger.
As such, the cover must be securely attached to one or both of the dashboard and the air bag housing. While some dashboards may be sufficiently rugged to provide an attachment point for the cover, it is typically preferred to attach the cover to the air bag housing, which is in turn securely connected to a structural member of the vehicle behind the dashboard. The need for strength in the connection between the cover and the housing has often resulted in complicated connection schemes.
An example of this is shown in U.S. Pat. No. 5,186,492 to Wright et al. In the arrangement of Wright the cover includes flanges which are riveted to the housing. This riveting process is of course time consuming and costly. U.S. Pat. No. 5,383,681 to Sato shows cover flanges which include tabs to mate with slots in the housing. However, Sato then places a reinforcement plate over the flanges and rivets through the plates and flanges, using even more material, adding more weight, and increasing the number of assembly steps.
A further problem with these prior art connections is that the cover is rigidly fixed with respect to the housing. As noted above, the housing is typically secured to a structural member behind the dashboard. If the cover is rigidly fixed to the housing, the cover is therefore rigidly fixed to the structural member. Since the cover is typically intended to be a flush continuation of the dashboard, the size tolerances on the structural member, housing, cover and dashboard must all be very tight, or the cover will not have the proper flush placement.
This problem of cover positioning, as well as the problem of a complicated connection between the cover and housing, is partially addressed in U.S. Pat. No. 5,303,951 to Goestenkors et al. In this patent the housing is secured to a structural member, and is formed of sheet metal. Along both lateral edges there are provided several tabs, struck from the sheet metal on one edge and formed by bending the sheet metal on the other edge. The cover has a depending skirt with slots for mating with the sheet metal tabs. On a first of the lateral edges these slots are oversized to permit the cover to float with respect to the housing. To secure the cover, the depending skirt also includes tabs which engage the dashboard. In addition to the cover, the housing also engages the dashboard on the second of the lateral edges.
While this arrangement overcomes some problems of the prior art, numerous problems remain. For example, while this arrangement provides some relief from tolerance build-up causing cover positioning problems, these problems still remain on the second lateral edge of the cover, which does not float. Furthermore, while riveting is not used, the relatively low strength of struck or bent sheet metal tabs to secure the cover causes safety concerns. Additionally, while the tabs and slots do not require riveting, there is a complicated translation-rotation motion required to secure the cover to the housing. Beyond this, a complex translation-rotation movement is also required to secure the module to the dashboard. Finally, this arrangement requires that the cover be secured to the housing before this completed module is attached to the dashboard.